1. Field of the Invention
This invention relates to a process for producing an internal-oxidized alloy or a shaped article thereof.
2. Description of the Prior Art
For the production of internal-oxidized alloys, the following process has heretofore been known: At least two metals are mixed by, for example, a melting method to obtain an alloy consisting of a matrix metal having contained therein at least one other metal in a total amount of not more than 20% by weight based on the weight of the alloy; the alloy is contacted, at its outside, with a metal oxide powder as an internal-oxidizing agent; and in this state, the alloy is heated to a temperature close to the melting point of the matrix metal to selectively oxidize only at least one metal other than the matrix metal present in the interior of the alloy (this treatment is referred to hereinafter as selective oxidation treatment).
The internal-oxidized alloy thus obtained contains a high-strength metal oxide (or metal oxides) in the form of fine particles in the matrix metal, and the fine particles of metal oxide(s) prevent the progress of rearrangement. Therefore, the internal-oxidized alloy, has an increased tensile strength as compared with the alloy before the selective oxidation treatment, and this high strength is retained even at high temperatures close to the melting point of the matrix metal. Because of these excellent characteristics, attention is drawn to the internal-oxidized alloy particularly as a material requiring both mechanical strength and heat resistance, such as dies for rubbers and plastics, turbine blades, electrical contacts and the like.
Such internal-oxidized alloys have the characteristics of the matrix metal as such together with excellent mechanical strength and heat resistance as discussed above, and hence, the characteristics of the matrix metal can be utilized as such. Therefore, various applications of the alloys are expected. Specifically, an internal-oxidized alloy obtained from an alloy in which the matrix metal is copper has a high electric conductivity and thermal conductivity which is equivalent to copper and simultaneously has an excellent dynamic strength and heat resistance. Therefore, said internal-oxidized alloy is expected to be used as a high temperature-resistant, electrically conductive material, a heat-sink material or the like.
The conventional process for producing an internal-oxidized alloy, however, has the following disadvantages: (1) In the selective oxidation treatment, it is necessary to heat the starting alloy to a temperature close to the melting point of the matrix metal from the exterior, and hence, the energy efficiency is low, the production cost is high, and the process is disadvantageous in mass production.
(2) The selective oxidation treatment utilizes the release of oxygen due to the thermal reaction of a metal oxide power which is an internal-oxidizing agent and diffusion of the released oxygen into the interior of the alloy material. Accordingly, direct control of the oxidation reaction is difficult, and the rate of the oxidation reaction is very low. In addition, the diffusion of the released oxygen into the interior of the alloy material governs the rate of oxidation reaction. Therefore, a long period of time is required to internal-oxidize a large size of alloy, and in many cases, the internal oxidation is actually impossible. PA0 (3) After the selective oxidation treatment, it is necessary to separate the internal-oxidized alloy from the powder of internal-oxidizing agent. The starting alloy can be used in the form of particles which can be effected in a high rate in the selective oxidation treatment, and the alloy particles can be subjected to selective oxidation treatment, followed by molding and sintering the resulting internal-oxidized alloy in the form of particles to obtain molded articles of the internal-oxidized alloy. In this case, however, both the internal-oxidized alloy and the internal-oxidizing agent are in the form of particles, and hence, separation of the internal-oxidized alloy from the internal-oxidizing agent after the selective oxidation treatment is very difficult.